Method of making an omega-shaped annulus



| E. GENENS ET AL 3,518,861

METHOD OF MAKING AN OMEGA-SHAPED ANNULUS Filed July 26, 1968 July 7, 1970 3 Sheets-Sheet 1 In 2/612 iars Lyle E. GefzeflS R 19 8/; If Z 119 KM flfofflgy July 7, 1970 GENENS ET AL 3,518,861

METHOD OF MAKING AN OMEGA-SHAPED ANNULUS Filed July 26, 1968 5 Sheets-Sheet 2 Fi -E I m/erifans E [e E. 6 176175 Robe/'6 Klefi tar/7g y 1970 L. E. GENENS ET AL 3,518,861

METHOD OF MAKING AN OMEGA-SHAPED ANNULUS Filed July 26, 1968 3 Sheets-Sheet 5 Inventors L yle 5. Gene/2,

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Avior/22y United States Patent 3,518,861 METHOD OF MAKING AN OMEGA-SHAPED ANNULUS Lyle E. Genens, Mokena, and Robert Kleb, Downers Grove, Ill., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed July 26, 1968, Ser. No. 747,904 Int. Cl. B21d .15 /06 US. Cl. 72-59 1 Claim ABSTRACT OF THE DISCLOSURE An omega-shaped annulus is formed from a short tube of large diameter by alternate steps of expanding the tube by pressure fluid and of shortening the tube with the fluid at zero pressure. The apparatus for shortening the tube is of moderate size, because the pressure fluid is at zero pressure during the shortening steps.

Contractual origin of the invention The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

Background of the invention This invention relates to the shaping of metal. More particularly, it relates to the forming of an omega-shaped annulus from a metal tube.

The omega-shaped annulus or bellows that is formed by the process of the present invention has a thin wall and a large diameter and is to constitute a flexible seal between a piston and walls of a 12-foot bubble chamber used with a particle source such as the Zero Gradient Synchrotron, of Argonne National Laboratory, Argonne, Ill. The piston keeps a liquid such as hydrogen in the bubble chamber slightly above the vapor pressure. When particles from the Zero Gradient Synchrotron enter the chamber, the hydrogen pressure is momentarily relieved by movement of the piston with respect to the bubble chamber, with the result that the hydrogen boils along paths taken by the particles. The resultant trails of tiny bubbles are photographed for future study and analysis. The omega-shaped annulus connecting the piston and the chamber permits the piston to move. It is highly desirable that the expanded or loop portion of the omega be as round or circular as possible, for such a shape significantly increases the life of the annulus.

The forming of an omega-shaped annulus from a tube is faced with two big problems. It is difficult to expand the loop of the omega uniformly and without wrinkles. A hydraulic press needed to handle the forming operation must be of tremendous size if conventional forming methods are used.

The method of the present invention avoids these two difficulties. According to the present invention, the tube used to form the omega-shaped annulus is expanded and shortened in such a way that wrinkling is avoided. Moreover, during the shortening steps the hydraulic pressure used to expand the tube is reduced to zero, and so the size of the device used to shorten the tube is greatly minimized.

Summary of the invention The present method, which transforms a short tube into an omega-shaped annulus, comprises a series of steps of alternately expanding the tube except at its ends by low fluid pressure and shortening the tube by endwise force with the fluid at zero pressure and a final step of expanding the tube at high fluid pressure.

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Brief description of the drawing FIG. 1 is an elevational view, with parts broken away in section, of an apparatus used to carry out the novel method of the present invention;

FIG. 2 is a sectional view showing a bubble chamber, a piston, and an omega-shaped annulus connecting the piston and chamber;

FIG. 3 is a fragmentary sectional view showing the tube after a first expansion step;

FIG. 4 is a fragmentary sectional view showing the tube after a later expansion step;

FIG. 5 is a fragmentary sectional view showing the tube after a next-to-final expansion step; and

FIG. 6 is a horizontal sectional view taken on the line 6--6 of FIG. 1.

Description of the preferred embodiment The novel method of the present invention is employed to convert a short tube 20 of large diameter, shown in FIG. 1, to an omega-shaped annulus 21, shown in FIG. 2. The annulus 21 and two rings 22 to which it is welded form a flexible sealed connection between a bubble chamber 23 and a movable piston 24.

As shown in FIGS. 1, 2 and 6, the apparatus for carrying out the present invention comprises a circular cylinder 25, a base member 26 of ring shape, and an upper movable member 27, also of ring shape. The upper member 27 has sliding sealing relation with the exterior of the cylinder 25 and is carried by a framework 28. The framework comprises a lower ring 29, an upper ring 30', and a circular shell 31 secured to and between the rings 29 and 30.

The lower ring 29 of the framework 28 is secured to the upper member 27, and the framework is carried on a plurality of vertical threaded rods 32, which are distributed about the framework and may be 17 in number. The rods 32 are distributed about the upp r ring 30 and extend through openings therein. The framework 28 is fixed against movement with respect to the rods 32 by upper nuts 33 and lower nuts 33a which are threaded on the rods 32 and engage the top and bottom, respectively, of the upper ring 30. There is an upper nut 33 on each rod 32. Only three of the rods 32 carry lower nuts 33a; these three rods are distributed about the upper ring 30 in generally equally spaced relation to one another, as shown in FIG. 6. Only three lower nuts 3301 are required, since they merely support the weight of the framework 28. On the other hand, 17 upper nuts 33 are required, one for each rod 32, since the upper nuts resist the considerable upward forces exerted on the framework 28 by the pressure fluid applied between the tube 20 and cylinder 25, as will be described presently.

The framework 28 is braced by webs 34 and stiifeners 35. The webs 34 extend radially outward from the shell 31 and are welded to the shell and the rings 29 and 30. The stiffeners 35 extend radially inward from the shell 31 and are welded to the shell and the upper ring 30.

The rods 32 are distributed about the interior of the cylinder 25 and extend through tubes 36 at the interior of the cylinder 25. The rods 32 are fixed against movement with respect to the cylinder 25 by nuts 37 threaded on the lower ends of the rods against the base member 26, and by nuts 38 threaded on central regions of the rods against the upper ends of the tubes 36. A concrete mass 39 is provided which reinforces the cylinder 25 against internal collapse and embeds the tubes 36 to fix them with respect to the cylinder 25.

Threaded rods 40, which may be three in number, are distributed about the inside of the cylinder 25 in tubes 36. Nuts 41 and 42 are threaded on the rods 40 against the base member 26 and the upper ends of the tubes 36 so as to place the rods 40 in considerable tension. The result is that the base member 26 is pressed very firmly against the cylinder 25 and no leakage of pressure fluid can occur between the cylinder and base member from an annular space 43 formed between the cylinder and the tube 20. A ring seal 44 located in a groove in the base member 26 acts between the base member and the cylinder 25.

The end portions of the tube 20, which overlap the interior of the rings 22 are welded thereto. Thereafter the assembled tube 20 and rings 22 are applied to the present apparatus as shown in FIG. 1. The lower ring 22 is secured to the base member 26 by screws 45 which are distributed about the base member and extend therethrough into threaded engagement with the lower ring. A ring seal 46 located in a groove in the base member 26 acts between the base member and the lower ring 22. The upper ring 22 is secured to the upper movable member 27, and the member 27, to the lower ring 29, by screws 47 which are distributed about the member 27 and extend through the lower ring 29 and the member 27 into threaded engagement with the upper ring 22. Ring seal 48 and ring seal 49, which are located in grooves in the member 27, act, respectively, between the member 27 and the upper ring 22 and between the member 27 and the cylinder 25.

At the outset, when the assembled tube 20 and rings 22 are being applied to the present apparatus, the framework 28 is held in the elevated position of FIG. 1. Now the lower nuts 33a are screwed down away from the upper ring 30 a small amount. The tube 20, being straight and unbowed, is stiff enough to hold up the framework 28 and prevent the upper ring 30 from following the nuts 33a. Next, pressure fluid, which may be oil, is applied to the annular space 43 between the tube 20 and the cylinder 25 and, as shown in FIG. 3, slightly expands the tube 20 except at its end portions, which lie within the rings 22. As the tube 20 is thus expanded, it is shortened in length and brings the framework 28 down. Thus the upper ring 30 descends and again engages the lower nuts 33a. Presumably the tube 20 will have expanded sufliciently for an operator to judge that the step of shortening the tube 20 at zero fluid pressure may be carried out without likelihood of inward buckling of the tube. If the operator judges the expansion to be insuflicient, a further expansion is performed by increase of the fluid pressure in the space 43 and a screwing down of the lower nuts 33a away from the upper ring 30.

Now the pressure of the fluid in the annular space 43 is reduced to zero, and the lower nuts 33a are screwed down away from the upper ring 30. The tube, being expanded, is no longer able to support the framework 28 and so becomes shortened as the framework 28 moves down by its own weight. Contact is reestablished between the upper ring 30 and the lower nuts 33a. Next, the upper nuts 33 are screwed down to the upper ring 30. Theoretically with zero pressure in the annular pace 43, the upper ring 30 will follow the lower nuts 33a in their downward adjustment, but as a practical matter, the upper movable member 27 may jam on the cylinder 25, because they are to seal one against the other. In this event, the upper nuts 33 must be screwed down against the upper ring 30- to force it down.

Now the step of applying pressure fluid to the annular space 43 is repeated. The lower nuts 33a are rotated down away from the upper ring 30 of the framework 28. The pressure fluid will expand the tube 20 again, and the tube will decrease in length again with such expansion and as a result of the weight of the framework 28, which moves down to reestablish contact between the upper ring 30 and the lower nuts 33a. The point will be reached, perhaps in the first step of expansion with pressure fluid, or perhap in a later step, when the upward force exerted by the pressure fluid in the annular space 43 aaginst the region of the upper movable member 27 between the cylinder 25 and the upper ring 22 and against the expanded portion 4 of the tube 20 is at least equal to the weight of the framework 28 and the frictional force between the upper movable member 27 and the cylinder 25. At this point the upper ring 30, during an expansion step, will no longer follow the lower nuts 33a as they are screwed down, but will remain pushed up against the upper nuts 33. This is why it is necessary to make sure that before the start of each expansion step, the upper nuts 33 are screwed down against the upper ring 30.

Now the step of reducing the length of the partially expanded tube 20 with the fluid in the annular space 43 at zero pressure is repeated, being carried out by downward movement of the framework 28 either through its weight or screwing-down of the upper nuts 33 against the upper ring 30 of the framework.

The steps of expansion'with fluid pressure and shortening at zero pressure of the fluid are repeated alternately on the tube 20 until, as shown in FIG. 5, a next-to-final form is reached in which the length is that of the omegashaped annulus 21 of FIG. 2, but the expanded section is not circular as shown in FIG. 2 but flattened into an ellipse having its long axis parallel to the axis of the tube 20 and its short axis radial of the tube. The aforementioned expansion steps are carried out at increasing fluid pressures all relatively low.

Now a final expansion step is carried out at a relatively high fluid pressure so that the ellipse of the tube 20, as shown in FIG. 5, is transformed into the circle of the annulus 21, shown in FIG. 2.

It was mentioned in the second paragraph above that the next-to-final form of the expanded section of the tube 20 is that of an ellipse with the long axis parallel to the tube axis. The same is true of earlier forms of the expanded section of the tube 20 an example of which is shown in FIG. 4; these forms are also elliptical, with the long axis parallel to the tube axis. These forms are elliptical, because the expansion steps employed to produce these forms are performed at relatively low pressures. Because these pressures are low, there is a minimum of stretching beyond the elastic limit and of work-hardening resulting therefrom. There is also a minimum of springback, i.e., tendency for the end portions of the tube 20 to be pushed apart. Because these forms are elliptical, there is little or no tendency of any portion of the expanded section of the tube 20 to decrease in diameter during the shortening steps. Consequently, there is little or no tendency of the expanded section to wrinkle during the shortening steps. Wrinkles could be almost impossible to remove.

Because work-hardening is kept to a minimum before the final expansion step, the round or circular shape of the expanded or loop portion of the annulus 21 when considered in the longitudinal section of FIG. 2, can be achieved in the final expansion step. Such a round or circular shape assures the annulus 21 a long life, because it greatly increases the number of flexures to which the annulus 21 can be subjected without rupturing.

Ideally the expanded section of the tube 20 after the next-to-final expansion step and the preceding expansion steps would be quite flat; that is, the ellipses in which the expanded section are successively formed would have their long axes quite long and their short axes quite short. As a pracical matter, this condition cannot be reached because of the shape of the rings 22, for the expanded section of the tube 20, if flattened beyond a certain point, will come into contact with the regions of the rings 22 outward of their thin ends during the expansion step, and will be damaged. Controlled flattening of the ellipses that the expanded section of the tube 20 successively assumes is achieved by gradual increase of the fluid pressure used for expansion from one expansion step to another including the next-to-final step.

At this point, it becomes appropriate to describe and discuss the shape of the rings 22. It will be observed that each ring 22 is generally shaped like a right triangle with a concave hypotenuse. This shape makes the rings 22 able to stand, without distorting, the pressure of the fluid employed to expand the tube 20. The curvature and thinness of the inner or facing ends and the concave hypotenuse of the rings 22 enable the tube to be shortened and expanded without damage. Because the facing ends of the rings 22 are curved, the tube 20 can expand over and in contact with the inner ends without damage. Because the outer surface of each ring 22 is concave and like the hypotenuse of a triangle, the expanded section of the tube 20 clears the outer surface during shortening of the tube and additional expansion of the expanded section and so avoids being damaged by contact with the outer surface.

As previously stated, the steps of shortening the tube by downward adjustment of the framework 28 are carried out with the pressure of the fluid in the annular space 43 between the tube 20 and cylinder 25 at Zero. Because of this, the size of the present apparatus is kept relatively small, because less force is required to adjust the framework 28 against zero pressure in the space 43 than against some elevated pressure in that space.

The process of the present invention was performed on a tube 20 which was formed of #316 stainless steel and had a length of 42.25", a thickness of .060", and a diameter of 126". The rings 22 were of #316 stainless steel. The length of each end portion of the tube 20 overlapping the associated ring 22 Was 3.5". The very end of each end portion was joined to an internal rib in the associated ring 22 by fission welding. The length of the portion of the tube 20 between the rings 22 was 35.25. In the completed annulus 21 the distance between the rings was 2.562", the center of the circle in which the expanded section was formed was on a diameter of 140", and the diameter of the expanded section was 150.5, and the length of the annulus was 9.75". As shown in FIG. 5, after being subjected to the next-tofinal expansion step and before being subjected to the final shortening step, the tube 20 had a length of 10.5, the distance between rings 22 was 3.312", and the diameter of the expanded section was 148.25". The relatively low pressure of the fluid used to expand the tube 20 was increased in steps from 39 lbs./in. in the. first expansion step to 205 lbs/in. in the next-to-final expansion step. The relatively high pressure of the fluid in the final expansion step was 800 1bs./in.

The present process is obviously applicable to the expanding of tubes that are larger and smaller in diameter than the tube specified in the preceding example. The process has been successfully employed on a tube of a few inches in diameter as well as one of 2 foot diameter. Clearly it can be carried out on a tube of 20 foot diameter;

6 the only requirement is an apparatus of s-ufiicient diameter.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of making an omega-shaped annulus of a substantially circular cross section from a tube, including the steps of:

(a) holding said end portions of the tube against outward expansion and movement away from each other while permitting unrestrained outward movement of the center portion of the tube;

(b) expanding the center portion of the. tube between said end portions outwardly by pressure applied uniformly throughout the interior of the tube while continuing to hold said end portions against outward expansion and movement away from each other;

(e) shortening the tube by moving said end portions toward each other at zero pressure within the tube;

(d) performing the expansion of step (b) in a series of steps and the shortening of step (c) in a series of steps, said expanding steps alternating with said shortening steps with the first expanding step occurring before the first shortening step;

(e) continuing steps (a) to (d) until said end portions are at their final desired positions with said outward expansion of the center portion of the tube being less than the final shape of the annulus;

(f) again expanding the tube except at said end portions to the final desired omega shape by pressure applied uniformly throughout the interior of the tube while holding the end portions against said expansion and in said final desired positions with said center portion of said tube being unrestrained.

References Cited UNITED STATES PATENTS 1,702,047 2/ 192-9 Ftulton et al. 72-59 2,615,411 10/1952 Clevenger et a1. 7260 2,631,640 3/1953 Zallea 72-58 2,756,804 7/ 1956 Schindler et a1 7259 FOREIGN PATENTS 1,234,706 5/ 1960 France.

1,120,409 12/1961 Germany.

RICHARD J. HERBST, Primary Examiner US. Cl. X.R. 7262 

